Within the framework of receivers of satellite signals serving for location, the presence of potential slowly varying multipaths of high level degrades the reception of the location satellite signals. This degradation in precision is due in particular to the disturbance, in an inhomogeneous manner, of the measurements of the code phase and of the carrier phase of the signals originating from the satellites. Within the framework of marine applications, these multipaths are caused by the reflection, on the structures of the ship or on the surface of the water, of the satellite signals. Still within the framework of marine applications, the satellite location systems for which the degradation of the precision is the most problematic are, for example, the systems used to carry out deck landings.
In order to improve satellite signals reception performance, in the presence of multipaths, it is known to add a spatial filtering. This spatial filtering may be carried out using a directional reception antenna. These antennas are known by the acronym “FRPA” for Fixed Radiated Pattern Antenna. These antennas make it possible to achieve a compromise between the following two processing operations:    1) detection of the satellite signals (the latter generally arriving with an angle of elevation of typically greater than 5°) and    2) rejection of the multipaths and sources of interference (the former generally arriving with an angle of elevation of typically less than 10°).
These antennas are of relatively reduced cost. These are for example antennas known as “Choke-ring” or antennas of helical type. The major drawbacks of antennas with fixed radiation pattern of FRPA type are that the compromise between the detection of the satellite signals and the rejection of the multipaths and sources of interference is very difficult to achieve at low elevation, and also that such antennas with fixed radiation pattern do not allow adaptation of the receiver to modifications of the local reception environment, and this may involve constraints on the installation of the antenna.
It is also known in the prior art to protect the antenna by virtue of mechanical structures known as “IMLP” for “Interference Multipath Local Protection”. These mechanical structures allow better mastery of the reflections. But such structures exhibit the major drawback of being bulky, typically a diameter of 5 to 10 meters and a height of 2 to 3 meters, of being expensive because of the absorbent materials used and of not contributing significantly to interference reduction.
It is also known in the prior art to carry out frequency and temporal filtering. This filtering is carried out by a device placed in the receiver. The type of filtering device used generally depends on the nature of the disturbance. In order to suppress interference it is known to use an analogue filtering of radio frequency type (in order to suppress the interference received outside of the band of the useful signal), or to carry out a filtering on the amplitudes known by the term “pulse-blanking” (or “pulse blocking”) in the case where the interference is pulsed and received within the band of the useful signal or else a narrowband frequency-wise digital filtering. The difference between radio frequency filtering and frequency-wise digital filtering is that the former is generally performed on the analogue signal at its reception frequency with the aid of discrete filters of ceramic or “SAW” (“Surface Acoustic Wave”) type, whereas the frequency-wise digital filtering is carried out only once the signal has been digitized and sampled, therefore at lower frequency (generally at the intermediate frequency, “IF”). Frequency-wise digital filtering permits notably adaptive filterings which are not achievable in analogue mode and make it possible to reject interference received in the useful reception band. In order to suppress the disturbances caused by multipaths, use is made of estimators of time received (also known as code discriminators) adapted to the deformations induced on the correlation function, such as, for example, NC discriminators (standing for “Narrow Correlator”), double delta discriminators (presented for example in the reference patent FR 2 742 612), MEDLL discriminators (standing for “Multipath Estimating Delay Lock Loop”). It is also possible to use the “SAGE” scheme (standing for “Space-Alternating Generalized Expectation Maximization”). However, on account of their specialization, these techniques are optimal only within a restricted domain of assumptions relating to the nature of the disturbance. These techniques therefore require the implementation of as many dedicated algorithms as types of different disturbances. This impacts the quality of the measurements determined on the basis of the signals received, notably the stability of the phase biases and the coherence between the code phase and the carrier phase. Moreover, this large number of algorithms complicates the step of validating the performance of the location system.
It is also known to use adaptive spatial processing based on a multiple antenna (for example the processing known by the term “CRPA” for “Controlled Reception Pattern Antenna” or by the term beam-forming antenna). A multiple antenna is an antenna consisting of a plurality of elementary antennas. This processing makes it possible to adapt the reception pattern of the antenna, automatically and without a priori knowledge of the configuration of the installation site (in particular without knowledge of the angle of elevation of the direction of arrival of the multipaths and of the interference). This adaptation makes it possible to maximize the reception power of the direct paths and to minimize the reception power of the reflected paths and of the interference. However this processing exhibits the drawback of increasing the complexity of the antennas and of the various elements performing the processing. Moreover this processing requires the calibration of the analogue elements of the receiver. The elements to be calibrated are in particular the antennas and the various elements of the radio frequency chain.